In previous generations of computer hardware and computer systems, a variety of different types of parallel busses were employed for interconnecting components, such as interconnecting peripheral I/O devices to a processor-and-memory bus through host bridges. Initially, busses comprising parallel signal lines to enable simultaneous transfer of bytes, 16-bit words, 32-bit words, or 64-bit words, provided higher data-transfer bandwidths than serial communications media, in which bit values are transferred consecutively, one after another, and coalesced by a receiving port into bytes, 16-bit words, 32-bit words, or 64-bit words. However, at high clock rates, signal skew between the parallel signal lines in a bus can become an increasingly difficult problem, and, as the densities of features within microprocessors and other integrated circuits have decreased, the large number of pins needed to connect an integrated-circuit component with a parallel bus represents an increasing cost and spatial constraint relative to processing power. As a result, serial communications media can now provide greater data-transfer bandwidths, are easier to incorporate into systems, place fewer constraints on integrated-circuit design and packaging, and are, in addition, more economical, than the older parallel busses. Older bus-based communications media, including the peripheral component interconnect (“PCI”) and advanced technology attachment (“ATA”) are being replaced by faster, more economical serial communications media, such as PCIe and SATA.
The process by which older technologies are replaced with newer technologies is generally gradual, as a result of which efforts are made to incorporate backwards compatibility in the newer technologies. For example, the newer PCIe provides backwards-compatibility features so that older components, designed to interface with PCI-based components, can interface with newer PCIe-based components. However, despite the efforts to provide for backwards compatibility during the introduction of newer technologies, problems arise. As one example, although newer PCIe serial communications media and controllers provide emulation of multi-dedicated-pin-and-trace-based interrupt mechanisms used in PCI communications media using messages transmitted through the newer serial communications media, new PCIe-compatible peripheral devices, such as I/O-device controllers, may fail to implement older PCI interruption modes. Although the newer PCIe-based devices that do not support older PCI-based interrupt modes correctly interoperate with computer systems designed to support PCIe-based components, such devices may not function correctly in older computer systems retrofitted with PCIe interconnects, despite being compatible with the PCIe interconnects. Designers, manufacturers, vendors, and users of computer systems that, during technology transition, incorporate both older-technology components and newer-technology components therefore continuously recognize the need for methods and devices to facilitate bridging of incompatibilities between newer-technology components and older-technology components, such as incompatibilities between operating systems and basic-input-output-system (“BIOS”) layers designed to interface with older-technology components that continue to be used in computer systems that incorporate, or connect to, newer-technology components.